Organic Light-Emitting Diodes (OLEDs) as a type of current-type light-emitting elements have become the mainstream display elements of the current display device, because of its thin, fast response, high contrast and other characteristics. OLED can be classified into the passive matrix driven OLED (PMOLED) and the active matrix driven OLED (AMOLED) according to driving methods. AMOLED has advantages such as short driving time, low power consumption, wide viewing angle, etc., and thus is applied to television, tablet and other device increasingly.
With the development of high-definition display technology, requirements to digital-to-analog conversion (DAC) performance in video processors are also getting higher and higher, usually requiring more than 10 bits. The current structure of the video processing DAC mainly includes a current steering and a resistor string voltage division type. Conventional current steering has characteristics such as high speed, high precision and so on. However, when the current steering is used to drive video transmission, the DAC output impedance must be equal to the characteristic impedance of the transmission line in order to suppress signal reflection. That is, the source current is twice that of the signal circuit, introducing higher power consumption. The resistor string voltage division type has advantages such as simple structure, small glitches and good linearity. However, the accuracy of the resistor voltage division type is mainly determined by the matching of the resistor string. In a general digital process, the resistor voltage division type can only reach about 8 bits.
For a general large-size AMOLED source driver, there are hundreds or even thousands of DACs per column driver circuit. Thus, the area of the DACs greatly affects the area of the entire driver chip, and the total area occupied by the DACs on the entire chip is usually as high as 60%-70%. Therefore, it is desirable to optimize the DAC structure and reduce the switch area while ensuring accuracy.